I'd have to disagree with all the people recommending SSRIs. The side effects these drugs have are very serious. High School was a hard time for my stutter as well. My advice is to stop avoiding all these situations. If you can give into them, you come back the other end. Accept that you stutter and remind yourself you will do your best in every situation, as it comes. You don't need to think about speaking beforehand. Have you sought out speech therapy? Do you do any practices on a daily basis? Have you tried morning meditation?